Abstract
Templated vapor synthesis and thermal annealing were
used to synthesize unsupported metallic Ru nanotubes with Pt or Pd
overlayers. By controlling the elemental composition and thickness of
these overlayers, we obtain nanostructures with very high alkaline
hydrogen oxidation activity. Nanotubes with a nominal atomic
composition of Ru0.90Pt0.10 display a surface-specific activity (2.4
mA/cm2) that is 35 times greater than that of pure Ru nanotubes at a
50 mV overpotential and ∼2.5 times greater than that of pure Pt
nanotubes (0.98 mA/cm2). The surface-segregated structure also
confers dramatically increased Pt utilization efficiency. We find a
platinum-mass-specific activity of 1240 A/gPt for the optimized
nanotube versus 280 A/gPt for carbon-supported Pt nanoparticles
and 109 A/gPt for monometallic Pt nanotubes. We attribute the
enhancement of both area- and platinum-mass-specific activity to the
atomic-scale homeomorphism of the nanotube form factor with adlayer-modified polycrystals. In this case, subsurface ligand and bifunctional effects previously observed on segregated, adlayer-modified polycrystals are translated to nanoscale catalysts.
